1. Field of the Invention
The present invention relates generally to network routers.
2. Description of the Related Art
Networks which are prone to experience disruptions are commonly referred to as Challenged Networks. The standard suite of Internet protocols assume that a stable end-to-end (E2E) path exists, that the maximum round trip time is not excessive, and that the packet drop probability is small. Networks that do not have these properties can be generally categorized as: highly-mobile networks, exotic media networks, military ad hoc networks and sensor networks.
Highly-mobile networks, at best, experience frequent route changes. They can also become partitioned unexpectedly, and in some cases an E2E path may never exist. Exotic media networks include satellite communications, deep space radio frequency (RF) links, acoustic modulation (used underwater) and line-of-sight (LOS) high-frequency radio or optical links. Networks using these kinds of links can experience very high round-trip times (RTTs), or outages due to environmental conditions. Military ad hoc networks are typically required to operate under hostile conditions in which enemy jamming can cause interruption, and the threat of eavesdropping may trigger periods of radio silence. Sensor networks often have very limited resources in terms of power and transceiver range. This can result in frequent link disruptions as well networks that are subject to partitioning. Airborne telemetry networks tend to fall into the highly-mobile category, as well as having power and weight constraints similar to sensor networks. A wide range of approaches has been developed, from modifying traditional IP-based protocols to be more tolerant of disruption and delay, to new architectures that operate as application overlays. One of the latter approaches to building a delay tolerant network (DTN), sometimes also referred to as a disruption tolerant network, is known as the bundling protocol architecture.
Delay tolerant networking is designed to minimize the impact of intermittent communication problems, as well as environmental limitations and anomalies. Delay tolerant protocols have been developed for a variety of applications. Some of the most prevalent protocols that fall into this category are the interplanetary networking (IPN) protocol and delay tolerate networking research group (DTNRG) protocol. Interplanetary Networking (IPN) presents environmental challenges that are orders of magnitude larger than those found in terrestrial networks due to the speed-of-light delay. Interplanetary systems do have the advantage that the delays are known very exactly due to the predictable motions of the planets. Eventually it was realized that IPNs are a subset of the broader category Delay Tolerant Networks, and that the work had terrestrial applications. The Internet Engineering Task Force (IETF) delay tolerant networking research group (DTNRG) protocols are largely a continuation of the work started in the internet protocol network (IPN) project, but extend the concepts to include networks with unpredictable round-trip times caused by a variety of challenges in addition to speed-of-light delays.
The DTNRG developed two main protocols, the Bundle Protocol and the Licklider Transmission Protocol (LTP). The Bundle Protocol is an overlay store-and-forward network that sends packages of application data over a wide range of underlying network types using a sequence of gateways that serve as nodes in the overlay network. This represents the mainstream approach within the DTNRG group. A prominent example implementation of the bundling protocol is the SPINDLE 3 system developed by BBN Technologies. Another DTN protocol is the LTP protocol. LTP is a point-to-point protocol that deals with individual long delay links by freezing timers that would otherwise expire before an acknowledgement was received. It relies on a lower layer scheduler to tell it exactly when and how much to transmit. Because it is only designed for dedicated point-to-point links LTP does not handle congestion or routing issues.
An alternative to using native IP or application-layer overlays in the telemetry network environment is to translate telemetry data into a custom protocol stack designed for highly dynamic environments. A recent approach using this method is the Airborne Network Telemetry Protocol (ANTP) suite which is composed of the AeroTP transport layer, the AeroNP network layer, and the AeroRP routing layer.
Developing non-IP protocols is a long-term approach to the problem that has benefits in reducing overhead associated with IP, as well as improving cross-layer information sharing. The downside is that retrofitting a network designed around IP-based protocols to use another network layer is difficult and costly.